Windshields and more frequently door glass is made of “laminated” glass which blocks up to 95% of damaging UV rays and provides the UV protection equivalent of 50+ SPF sunscreen.
Remaining auto glass in a vehicle is usually made of “tempered” glass. The UV transmittance can vary due to the makeup of the glass. See the chart below for which glass may perform best against UV light.
*Batch privacy is a dark grey glass – colorant is in the glass composition as opposed to a reflective coating which was used on Ford-Lincoln-Mercury vehicles prior to 1998 or 1999 model year (depending on vehicle). The older, “pyrolytic” privacy was a coated grey glass that had a mirrored inside surface and a “bronzish” appearance.
The ranges of transmittances above are due to differences in glass thickness for any given category of parts. Glass thickness typically ranges from 3.2 mm up to 4.8 mm for side glass, back windows and moonroofs; and 4.7mm to 6.0 mm for windshields. The thicker the glass, the lower the visible and UV transmittance. Carlite windshields produced after April 2001 have a UV light transmittance of just under 3%, meaning that 97% of the sun’s UV rays are blocked. This is equivalent to a sun protection factor (SPF) of 157.
**Windshields produced prior to 2000 model year had ultraviolet transmittance values of around 14% which equates to a SPF of 68.
Glass of any kind blocks all UVb, which is the most harmful ultraviolet light. The UV transmittances above show the total transmittance values for UVa and UVb.